The first report on a convenient synthesis of novel reactive amphiphilic polysaccharides

New amphiphiles with reactive tosylate groups and ionic sulfuric acid half esters based on the rod-like polysaccharide cellulose were designed via homogeneous tosylation followed by sulfation with the SO₃-pyridine complex in N,N-dimethylacetamide. At appropriate degrees of functionalization the polymers are soluble both in water and dimethyl sulfoxide, and they are promising starting materials for self-organizing systems.     

The first stereoselective synthesis of dendrodolide A

The first stereoselective total synthesis of natural product, dendrodolide A (1) is described from readily available (R)-propylene oxide and 3-buten-1-ol as starting materials. The synthesis was achieved in 10 steps with an overall yield of 19.1%. The key steps involved in the synthesis are Jacobsen hydrolytic kinetic resolution, epoxide ring opening with 2-allyl-1, 3-dithiane, Yamaguchi esterification, and ring-closing metathesis (RCM).     

A novel highly stereoselective synthesis of chiral 5- and 4,5-substituted 2-oxazolidinones

A novel highly stereoselective synthesis of chiral mono- and bicyclic 4- and 4,5-substituted 2-oxazolidinones starting from β-keto esters was developed. After bioreduction with S. cerevisiae the resulting homochiral β-hydroxy esters are transformed into their hydrazides. Treatment with NaNO₂/H⁺ then furnishes 2-oxazolidinones in high e.e. (∼99%) and d.e. (>99%). The ring formation proceeds via a highly concerted sextet rearrangement with full retention of configuration at the stereocentres. Enantiopure 1,2-amino alcohols can subsequently be obtained by saponification of the 2-oxazolidinone products.     

Highly stereoselective synthesis of novel alpha-haloenamides via a mild and efficient hydrohalogenation of ynamides

A highly stereoselective preparation of novel chiral (E)-alpha-haloenamides under mild conditions utilizing magnesium halide salts is described. This unexpected mild and efficient hydrohalogenation reaction highlights another synthetic utility of ynamides. [reaction: see text]     

The first stereoselective synthesis of optically active thiosulfinates

Treatment of optically active $\text{p}$-toluenesulfinamides (1) with thiols (2) in the presence of trifluoroacetic acid was found to give optically active $\text{p}$-toluenethio-sulfinates (3) with predominant inversion of configuration. Stereospecificity of this reaction varies from 30 to 80%. Some mechanistic aspects of the reaction are also discussed.     

The first stereoselective total synthesis of quinine.

The first entirely stereoselective total synthesis of (-)-quinine is reported.     

The first stereoselective total synthesis of nicotlactone A

Herein we report the first stereoselective total synthesis of nicotlactone A via acid catalyzed acetonide deprotection followed by intramolecular lactonization in one pot as the key step.     

The first stereoselective synthesis of (+)-nuciferol and (+)-nuciferal

Using (S)-benzyl 2,3-epoxypropyl ether (1), the first stereoselective synthesis of (+)-nuciferol (14) and (+)-nuciferal (16) has been achieved. Employing the same methodology an enantioselective synthesis of (+)--curcumene (17) is also described.     

(+)-saxitoxin: a first and second generation stereoselective synthesis

A stereoselective synthesis of the bis-guanidinium toxin (+)-saxitoxin (STX), the agent infamously associated with red tides and paralytic shellfish poisoning, is described. Our approach to this unique natural product advances through an unusual nine-membered ring guanidine intermediate 39 en route to the tricyclic skeleton that defines STX. The effectiveness of this strategy is notable, as only four steps are needed to transform 39 into the target molecule, including a four-electron alkene oxidation catalyzed by OsCl3. Construction of the critical monocyclic guanidine has been achieved through two channels, the first of which makes use of Rh-catalyzed C-H amination and highlights a novel class of heterocyclic N,O-acetals as iminium ion equivalents for crafting functionalized amines. A second route to 39 relies on a stereoselective acetylide dianion addition to a serine-based nitrone, thereby facilitating the preparation of STX in just 14 linear steps from commercial material.     

A novel synthesis of carbacyclin analogs via a stereoselective introduction of 15α-hydroxy group

(+/-)-6,9α-Methanoprostaglandin I₃, ($\text{2}$) and (+/-)-5,6-dihydro-6,9α-methano-6β-prostaglandin I₃, ($\text{4a}$) have been synthesized using a new method for the stereoselective introduction of the 15α-hydroxy group via a stereoselective electrophilic addition of phenyl-sulfenyl chloride to the enol ether ($\text{6}$) and ($\text{23}$) respectively.     

The first example of stereoselective self-assembly of a cryptand containing four asymmetric intracyclic phosphane groups

The rac stereoisomer of a novel cryptand containing two bridgehead nitrogen and four asymmetric phosphorus atoms in the 16-membered core cycle was obtained stereoselectively via the reaction of bis(mesitylphosphino)propane, formaldehyde, and meta-xylylenediamine in the course of a covalent self-assembly process.     

The first stereoselective total synthesis of lankanolide. Part 2

The seco-acid derivative designed by conformation calculation and lactonization experiment of model seco-acids was synthesized, and subjected to macrolactonization to afford the lactone derivative. The lankanolide was synthesized via several steps after the lactonization, and the synthetic lankanolide was confirmed to have the same physical data (NMR, mass, IR and αD) as the lankanolide prepared from lankamycin according to the reported method.     

The first stereoselective and the total synthesis of Leiocarpin C and total synthesis of (+)-Goniodiol

The synthesis of the styryl lactone Leiocarpin C has been achieved in a highly stereoselective manner using Jacobsen’s kinetic resolution, Sharpless asymmetric epoxidation and Sharpless asymmetric dihydroxylation as key steps. This is the first total synthesis of Leiocarpin C, and thus establishes for the first time the absolute stereochemistry of this natural product.     

Design,stereoselective synthesis and computational calculations of novel hybrid compounds via Pauson-Khand reactions

A series of novel chiral hybrid compounds between benzofuran and bicyclic cyclopentenone and also benzothiophene and bicyclic cyclopentenone have been designed and synthesized. Chiral enynes derived from enantiomerically enriched homoallyl and homopropargyl alcohols were converted into bicyclic cyclopentenone structures by intramolecular Pauson-Khand reactions. This strategy provides a facile access to various bicyclic cyclopentenones substituted with benzofuran or benzothiophene ring systems in good yields. In addition to the experimental work, the ground state geometries of the hybrid compounds were optimized using Density Functional Theory applications at the B3LYP/6-31G(d,p) level in order to obtain information about the 3D geometries and electronic structure.     

The first example of the stereoselective synthesis and crystal structure of a spirobicycloquinazolinone based on (–)‐fenchone and anthranilamide

The possibility of a single‐stage solvent‐free stereoselective synthesis of a spirocyclic compound from the natural bicyclic monoterpenoid (?)‐fenchone and anthranilamide has been shown for the first time. The molecular and crystal structure of (1R,2S,4S)‐1,3,3‐trimethyl‐1′H‐spiro[bicyclo[2.2.1]heptane‐2,2′‐quinazolin]‐4′(3′H)‐one, C₁₇H₂₂N₂O, was established by X‐ray diffraction though the chirality was assumed via the known reactant connectivity and ¹H and ¹³C NMR spectroscopy. It has shown that in the molecule, for steric reasons, there is an elongation of the Me₂C—C(N)N bond to 1.603 (5) Å. The formation of dimers via N—H…O=C hydrogen bonds with an interaction energy of 93.30 kJ mol^?1 and through cavities (33.7% of the unit‐cell volume) was established in the packing of the molecules. There are no π‐stacking interactions in the structure.     

The first synthesis of 7-prenylisatin

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The first example of macrocycles containing butterfly transition metal cluster cores via novel tandem reactions

A novel type of double butterfly, two mu-CO-containing dianions {[(mu-CO)Fe2(CO)6]2[mu-SCH2(CH2OCH2)nCH2S-mu]}2- (m1, n = 2, 3), has been synthesized from dithiol HSCH2(CH2OCH2)nCH2SH (n = 2, 3), Fe3(CO)12, and Et3N in THF at room temperature. While dianions m1 react in situ with CS2 followed by treatment with dihalide 1,4-(BrCH2)2C6H4 or 1,4-I(CH2)4I to give macrocyclic clusters [mu-SCH2(CH2OCH2)nCH2S-mu](mu-CS2ZCS2-mu)[Fe2(CO)6]2 (1a, n = 2, Z = 1,4-(CH2)2C6H4; 1b, n = 3, Z = (CH2)4), reactions of dianions m1 with (mu-S2)Fe2(CO)6 followed by treatment with dihalide 1,4-I(CH2)4I afford macrocyclic clusters [mu-SCH2(CH2OCH2)nCH2S-mu]{[Fe2(CO)6]2(mu4-S)}2[mu-S(CH2)4S-mu] (2a, n = 2; 2b, n = 3). The crystal structures of 1a and 2b are described.     

The stereoselective synthesis of novel macrolide antibacterial agents via an intramolecular 1,3-dipolar cycloaddition of azomethine ylide

An intramolecular 1,3-dipolar cycloaddition of azomethine ylide, generated in situ via the reaction of C12-glycinate derivative of macrolide with formaldehyde, provided a novel tricyclic macrolide. The high stereoselectivity of this [2+3] reaction was achieved by introducing a suitable directing group at C-6 position of macrolide.     

Highly stereoselective synthesis of novel cyclobutane-fused azanucleosides

Stereoselective syntheses of several 3-azabicyclo[3.2.0]heptane nucleoside analogues have been efficiently completed starting from a homochiral a,b-unsaturated-g-lactam. The target compounds were prepared by condensation of a common bicyclic acetate intermediate with pyrimidine and purine bases under modified Vorbrüggen conditions. The anti-HIV activity of the newly synthesized azanucleosides has been evaluated.     

Efficient stereoselective synthesis of novel steroid-polyquinane hybrids

A synthesis of steroid-polyquinane hybrids, a new class of molecular entities, is described. [reaction: see text]